ISLAMIC State will “inevitably” construct or acquire weapons of mass destruction, the former head of the British Army’s nuclear team warns.

The risk of an improvised nuclear bomb being detonated in a foreign city has “increased substantially” because of tensions with Russia, he claims.

Dr Hamish de Bretton-Gordon said the extremist jihadist group already had chemical weapons such as mustard gas and it is “only a matter of time” before it managed to launch an attack capable of destroying a substantial part of a city.

Bretton-Gordon, who formerly commanded the British Army’s Chemical Biological Radiological and Nuclear (CBRN) regiment, gave the stark warning as he addressed the Global Resilience conference in London on Thursday.

“Isis have made it known they want to acquire weapons of mass destruction,” he said.

“They run a sophisticated and successful psychological warfare campaign and are now basing that on CBRN weaponry – the ultimate weapon in the terrorist arsenal.”

IS already has control of unenriched uranium from stocks captured from Iraq’s University of Mosul.

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ISIS wish to acquire weapons of mass destruction

“The uranium they have is not weaponised but we know Isis have recruited scientists to develop chemical and nuclear weapons,” he said.

It costs £26million to buy a single kilo of highly enriched uranium, but IS “had the funds” and the inclination.

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Dr Bretton-Gordon said that, while cities in Iraq and Moscow were “extremely vulnerable”, Britain was more secure because of the “high quality” of its intelligence services.

Isis have made it known they want to acquire weapons of mass destruction

Dr Hamish de Bretton-Gordon

The FBI has already foiled four attempts by Russian organised crime gangs to supply radioactive material to jihadist extremists.

Russia racked up tensions recently when it pledged jets to support Syrian government ground troops fighting opposition groups and IS.

Dr Bretton-Gordon added: “The problem is that, for all Vladimir Putin’s bluster, Russia is not very effective militarily.

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Enriched uranium

“Not only is Moscow a target to extremists but its poor performance by its own intelligence agencies, as shown by the fact that it’s the FBI breaking up these attempts in eastern Europe, means the chances of Russian organised crime succeeding are much greater.”

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Vladimir Putin's bluster does not cover up the fact that Russia "is not very effective militarily"

His warnings come as Prime Minister David Cameron announced £5million for the Government’s new Counter Extremism Strategy to tackle extremist ideology and address “the segregation and feelings of alienation that can help provide fertile ground for extremist messages to take root”.